Image forming apparatus

Abstract

An image forming apparatus according to an embodiment includes a first roller arranged on a conveyance path of a sheet and a second roller arranged downstream of the first roller in the conveyance path. A control section calculates a deflection amount of the sheet nipped by the first roller and the second roller based on a conveyance speed of the sheet conveyed along the conveyance path. When the calculated deflection amount is smaller than a predetermined lower limit value, the control section increases the rotation speed of the first roller and decreases the rotation speed of the second roller.

What is claimed is: 
     
       1. An image forming apparatus, comprising:
 a first roller arranged on a conveyance path of a sheet; 
 a second roller arranged downstream of the first roller in the conveyance path; and 
 a control section configured to:
 calculate a deflection amount of the sheet nipped by the first roller and the second roller based on a conveyance speed of the sheet conveyed along the conveyance path, 
 when the calculated deflection amount is smaller than a predetermined lower limit value, increase the rotation speed of the first roller and decrease the rotation speed of the second roller, and 
 when the calculated deflection amount is greater than a predetermined upper limit value, decrease the rotation speed of the first roller and increase the rotation speed of the second roller. 
 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein
 the control section calculates the conveyance speed of the sheet based on the rotation speed of the first roller and the rotation speed of the second roller. 
 
     
     
       3. The image forming apparatus according to  claim 1 , further comprising:
 a first speed sensor configured to measure a speed of a surface of the first roller; and 
 a second speed sensor configured to measure a speed of a surface of the second roller, wherein 
 the control section calculates the conveyance speed of the sheet based on the speed measured by the first speed sensor and the speed measured by the second speed sensor. 
 
     
     
       4. The image forming apparatus according to  claim 1 , wherein
 the control section controls the rotation speed of the first roller and the rotation speed of the second roller according to a length of the sheet in a conveyance direction of the sheet along the conveyance path. 
 
     
     
       5. The image forming apparatus according to  claim 1 , wherein
 the control section controls the rotation speed of the second roller such that the rotation speed of the second roller does not exceed the rotation speed of the first roller. 
 
     
     
       6. The image forming apparatus according to  claim 1 , wherein
 the control section controls the rotation speed of the first roller such that the rotation speed of the first roller is not slower than the rotation speed of the second roller. 
 
     
     
       7. The image forming apparatus according to  claim 1 , wherein
 the first roller is a transfer roller for transferring a toner image to the sheet; and 
 the second roller is a fixing roller for fixing the toner image on the sheet. 
 
     
     
       8. The image forming apparatus according to  claim 1 , wherein
 the first roller is a register roller for adjusting the conveyance direction of the sheet before the sheet enters a transfer position on the conveyance path; and 
 the second roller is a transfer roller for transferring a toner image to the sheet at the transfer position. 
 
     
     
       9. An image forming apparatus, comprising:
 a register roller arranged on a conveyance path of a sheet; 
 a transfer roller arranged downstream of the register roller in the conveyance path; 
 a fixing roller arranged downstream of the transfer roller in the conveyance path; and 
 a control section configured to:
 calculate a deflection amount of the sheet nipped by two of the register, transfer, and fixing rollers based on a conveyance speed of the sheet conveyed along the conveyance path between the two rollers, 
 when the calculated deflection amount is smaller than a predetermined lower limit value, increase the rotation speed of one of the two rollers that is upstream, and decrease the rotation speed of the other of the two rollers that is downstream, and 
 control the rotation speed of the register roller, the transfer roller and the fixing roller according to a length of the sheet in a conveyance direction of sheet along the conveyance path. 
 
 
     
     
       10. The image forming apparatus according to  claim 9 , wherein
 the control section calculates the conveyance speed of the sheet based on the rotation speed of each of the three rollers. 
 
     
     
       11. The image forming apparatus according to  claim 9 , further comprising:
 a first speed sensor configured to measure a speed of a surface of the register roller; 
 a second speed sensor configured to measure a speed of a surface of the transfer roller; and 
 a third speed sensor configured to measure a speed of a surface of the fixing roller, wherein 
 the control section calculates the conveyance speed of the sheet between the register roller and the transfer roller based on the speeds measured by the first and second speed sensors, and the conveyance speed of the sheet between the transfer roller and the fixing roller based on the speeds measured by the second and third speed sensors. 
 
     
     
       12. The image forming apparatus according to  claim 9 , wherein
 when the calculated deflection amount is greater than a predetermined upper limit value, the control section decreases the rotation speed of the one of the two rollers that is upstream, and increases the rotation speed of the other of the two rollers that is downstream. 
 
     
     
       13. A method of controlling rotation speeds of first and second conveyance rollers that convey a sheet along a conveyance path, the second conveyance roller being arranged downstream of the first roller in a sheet conveying direction, the method comprising the steps of:
 determining a conveyance speed of the sheet conveyed along the conveyance path; 
 calculating a deflection amount of the sheet nipped by the first roller and the second roller based on the conveyance speed of the sheet conveyed along the conveyance path; 
 when the calculated deflection amount is smaller than a predetermined lower limit value, increasing the rotation speed of the first roller and decreasing the rotation speed of the second roller; and 
 when the calculated deflection amount is greater than a predetermined upper limit value, decreasing the rotation speed of the first roller and increasing the rotation speed of the second roller. 
 
     
     
       14. The method according to  claim 13 , wherein
 the conveyance speed of the sheet is calculated based on the rotation speed of the first roller and the rotation speed of the second roller. 
 
     
     
       15. The method according to  claim 13 , further comprising:
 measuring a speed of a surface of the first roller with a first sensor; and 
 measure a speed of a surface of the second roller with a second sensor, wherein 
 the conveyance speed of the sheet is determined based on the speed measured by the first speed sensor and the speed measured by the second speed sensor. 
 
     
     
       16. The method according to  claim 13 , wherein
 the first roller is a transfer roller for transferring a toner image to the sheet; and 
 the second roller is a fixing roller for fixing the toner image on the sheet. 
 
     
     
       17. The method according to  claim 13 , wherein
 the first roller is a register roller for adjusting the conveyance direction of the sheet before the sheet enters a transfer position on the conveyance path; and 
 the second roller is a transfer roller for transferring a toner image to the sheet at the transfer position.